Treatment of molten metals



United States Patent Ofifice 2,952,534 Patented Sept. 13, 1960 TREATMENT OF MOLTEN METALS James M. Quinn, 1347 San Luis Rey Drive, Glendale, Calif., and Ted A. Lundbergh, Redondo Beach, Calif.; said Lundbergh assignor to said Quinn No Drawing. Filed June 3, 1957, Ser. No. 662,994 5 Claims. (CI. 75-45) This invention relates generally to the purification of metals and particularly relates to a composition of matter and a process for deoxidizing, degassing, cleaning, and improving the ductility and machinability of molten metals.

This application is a continuationin-part of our copending US. application, Serial No. 470,824, filed November 23, 1954, now abandoned, entitled Treatment of Molten Metal; Ferrous and Non-Feirous.

Many proposals have been advanced for the degassing, deoxidization and cleaning of metals such as aluminum, copper, zinc, iron and alloys thereof, which involve the addition of certain substances to the metal while it is in its molten state. One of these proposals involves the addition of a plurality of carbon-containing briquettes which have various types of fluxes incorporated therein. These carbon-containing particles, While satisfactory in some instances, do not produce substantially deoxidized and degassed metals in the more extreme cases of metal impurity.

Bearing in mind the foregoing facts, it is a major o ject of the present invention to provide a composition of matter and process for the improved cleaning, deoxidation and degasification of molten metals.

Another object of the present invention is to provide a composition of matter for the improved cleaning of molten metals and for simultaneously cleaning the side walls of the crucible or furnace in which the melt is contained.

It is a further object of the present invention to provide a composition of matter, and a process, for the improved cleaning of molten metals wherein carbon-containing particles are employed for the deoxidation, degasification and cleaning in other respects, said carbon particles having imparted thereto a high degree of motion while within said molten metal to thereby clean, deoxidize and degasify said metal in an improved manner.

Still another object of the present invention is to provide a composition of matter, for the improved cleaning of metals which include the use of a plurality of light carbon-coated particles of extremely hard central core composition and of extremely small particle size, which are adapted to be intimately intermixed with and pass through the metal to be purified, the particles being maintained under a high degree of agitation.

Yet a further object of the present invention is to provide a composition of matter for reducing the buildup of oxides in the crucibles and furnaces containing a molten metal.

Another object of the present invention is to provide a composition of matter and a process for substantially increasing the ductility and machinability of metals.

Still another object of the present invention is to provide a composition of matter and a process whereby the homogenization or stabilization of alloys in a molten metal is substantially increased.

These and other objects of the present invention will become clearly understood by referring to the following description.

According to our invention, we have found that if an extremely small, hard, light and heat-resistant particle is coated with a thin layer of carbon and/or hydrocarbons, the particle thus produced is extremely advantageous in deoxidizing, degassing, grain-refining, homogenizing, and generally improving the ductility and machinability of the metal. Such a particle is also advantageous in simultaneously cleaning the crucible in which the metal is contained.

The terms carbon coating, carbon-coated particle, carbon-containing particle will be used hereinafter as including a substantially all-carbon coating, or a substantially all-hydrocarbon coating of a particle.

Referring specifically to the composition of matter employed in our invention, carbon-coated particles are utilized which have a very hard and chemically inert core. A preferred core is that which comprises 10% to 30% alumina and 70% to silica (SiO such core compositions ranging in hardness from 8 to 9 on a Mohs scale. The preferable size of the cores of the particles ranges from between 2 microns up to 200 microns so that they may become more intimately dispersed within the molten metal, as will be described in greater detail hereafter. The cores are usually spherical, ellipsoidal or oval in shape.

The carbon coating of the particles is obtained by heating the particles to preferably about 1300 F., then passing crude liquid petroleum over the heated particles thereby causing the vaporization of petroleum. The residue of the petroleum, consisting mostly of heavy hydrocarbons, envelops the particles forming a thin carbon coating, usually of the order of 26 microns, although sometimes it is much higher, for example 25 microns. It can thus be seen that the usual size rangein which the particles are employed may vary between about 5 microns up to about 225 microns.

The amount of carbon preferably deposited upon the particles varies on the average between 0.25 to 0.75% of the total weight of the particle. If the percentage of combustible hydrocarbons per particle is higher than 0.75%, it is possible that some carbon may react with the molten metal. The addition of carbon to the melt by such means is undesirable, and the hydrocarbon percentage is therefore maintained below 0.75%. On the other hand, it is found that the threshold value below which deoxidation of the molten metal does not take place is approximately 0.25%.

A specific example of a particle embodying our new composition of matter is set forth below:

Core 81.1% SiO 18.4% A1 0 Coating 0.5% hydrocarbons. Shape of particle Approximately spherical. Size of core Diameter=20 microns. Size of coating Thickness=4 microns. Size of particle Total diameter- 24 microns. Specific gravity of particle 2.4

The method of use of these particles varies in many respects, depending upon the particular metal to be purified, specific examples being set forth hereafter. However, the method step which is common to all metal purifications includes the step of contacting the lower portions of the molten metal with the bulk of the carboncoated particles, and will now be considered in detail.

The multiplicity of carbon-coated particles, upon being dispersed within the interior of the molten metal, by any of several methods to be described, reacts with the oxygen within the molten metal to release relatively large amounts of energy and relatively large volumes of gases. Due

apparently to the release of the heat energy, a high de-- gree of mechanical energy, both in linear and rotary motion, is imparted to the particles themselves. The increased mechanical energy of the particles is believed to be responsible for the improved cleaning, dross removal, de-slagging, and dispersal of alloys in the metal to thereby increase its machinability and ductility.

The conversion of the heat energy, released during combustion of the carbon coating, to the particle mechanical energy is believed to proceed in a manner analogous to the use of hydrocarbons as fuel in internal combustion engines. That is to say, the heat energy released in the immediate vicinity of each particle during combustion of the hydrocarbons is thought to be transmitted to these same particles by means of the gas expansion during the combustion process, just as the gases expand upon ignition in a cylinder and give a power thrust to a piston. The transfer of this heat energy to the particles thus substantially increases its mechanical energy, with the aforementioned advantageous results.

Further, the particle being very light (having a specific gravity generally of the order of between 2.2-2.6), rises through heavier molten metals throughout the period of combustion, and, in so doing, contacts a much greater volume of metal thereby substantially improving the homogeneity of steels and other alloy-containing metals, as well as forcing a substantially greater percentage of dross, slag and other impurities to the surface of the melt. Also, the high degree of mechanical energy imparted to the particles causes the particles to strike the sides of the crucible in which the melt is contained and to free the slag, dross and impurities encrusted thereon, thereby forcing these impurities to the surface. The particles, in striking the crucible walls, do not disintegrate or decompose because of their extreme hardness.

As mentioned, the size of the particles is below 225 microns. Thus, theoretically and in practice, over 16 million particles per square inch undergo the reactions above described. Aside from the differences in the mechanical energies of the particles of our invention as compared to those of the prior art, the tremendous number of particles introduced into a molten metal is found to substantially increase the removal of impurities, dross, etc. therefrom, as well as to increase the homogeneity or stability of the metal. The ductility and machinability of the material is thus substantially increased.

Further, the high energy imparted to each individual particle as it rises through the molten metal, in combination with the millions of similar high speed particles per square inch, renders the metal substantially free of dross, dirt and other foreign matter.

By way of contrast, it is found that if the matrix of our particle is employed alone, that is, without the carbon covering, the amount of dress, impurities, and the like rising to the surface of the melt is very small, and that further, an inconsequential amount of crucible side wall cleaning is obtained.

The particles upon reaching the surface of the melt are substantially entirely freed of any carbon and act as a sealer or cover for the melt, thereby protecting it from oxidation. The carbon-coated particles themselves can be initially spread upon the surface of a molten mass for the same protective purposes. In such a case, the carbon initially upon the particle will be oxidized, but the protective qualities or covering qualities of the particles are not lessened in any degree.

Since the reaction between the coating of the particle and the melt is essentially an oxidation reaction whereby carbon dioxide and water vapor is produced, it will be seen that no contaminating gases are produced by the process of our invention.

After the melt has been cleaned, it may be cast, extruded, rolled or fabricated in any other desired manner. Specific examples of the use of our composition of matter forspecific melts will now be described.

Example I In the purification of aluminum or aluminum alloys, approximately one third of a 100 pound batch of aluminum is melted in a suitable crucible at a temperature of approximately 1100 to 1200 F. One pound of the carbon-coated particles of our invention is used per hundred pounds of aluminum, and one-third of a pound of particles is folded into the melt in any suitable manner, for example with a skimming device. The second third of the aluminum is charged into the crucible and one half pound of the particles is poured onto the melt as it reaches the 1100 F. temperature.

The crucible is then charged with the balance of the metal and the remaining one-sixth of a pound of the particles is used as a cover and spread over the surface of the metal.

The slag and dross almost immediately commence to rise to the surface of the metal along with the particles, most of the particles being completely oxidized so that only the bare core appears at the surface. After the drossing action is substantially completed, which generally takes from but several seconds to about one minute, depending upon the condition of the melt, the impurities are then skimmed or raked from the top of the melt along with the bare particle cores and the surface of the melt is then covered by additional fresh carbon-coated particles to prevent further oxidation of the melt until it is ready to pour or ready for other uses.

Example 11 In purifying brass, four to six ounces of carbon-coated particles are used for each one hundred pounds of melt. One-third of the melt is charged to a suitable crucible and brought to its melting point. It is then covered with approximately of the required amount of the particles and the remainder of the melt is charged to the crucible. By charging the metal to the crucible in this manner, the particles are forced completely downwardly towards the bottom of the crucible and through the melt. The particles, upon rising, cause deoxidation of the melt as described, with resulting high particle energies and velocities whereby a high degree of stabilization and dispersion of the alloys in the metal and the rising of the dross, slag and other impurities of the top surface of the metal are produced.

The dross, slag and other impurities are skimmed olf as described with reference to Example I, and a cover of carbon-coated particles is placed on the surface of the melt to protect it from oxidation until further use.

Example 111 A high zinc base alloy is placed in an appropriate crucible and melted at a temperature of between 750 to 800 .F. Two ounces of carbon-coated particles per lbs. of melt are placed in a plunging cup and immersed from a point just below the surface of the metal, by means of a slow rotating action, to the bottom of the metal. The particles are not plunged immediately to the bottom in one operation because of the danger of excessive bubbling and splashing of the metal.

After the drossing, slagging and removing of impurities have been completed, the surface of the metal is then skimmed and covered with carbon-coated particles until ready for use.

Example IV In the purification of iron and steel two ounces of carbon-coated particles are placed in the bottom of an appropriate crucible for every one hundred pounds of molten metal poured into the crucible. The drossing action and alloy dispersion within the metal is very rapid. The dross is skimmed off and the melt is protected by a carbon-coated particle cover, as described.

From the foregoing examples, it will be seen that a variety of types of metals, both ferrous and non-ferrous,

can be treated by means of our new composition of matter, since once the carbon is burned oil from the particle due to its oxidation, the inner core of the particle is of such a composition as to be inert to the action of most metals, even in their molten state.

In all of the foregoing examples, the carbon content of the metal is not increased and the drossing and dispersing action is practically immediate.

While we have described in some detail a preferred embodiment of our invention, it will be understood that substantial changes and modifications may be made that lie within the scope of our invention. Hence, we do not wish to be limited by the embodiments described herein, but only by the appended claims.

We claim:

,1. A process for cleaning molten metals, which comprises: submerging a multiplicity of particles into said metal, said particles each having a core consisting essentially of -30% alumina and 70-90% silica, and a coating thereover selected from the group consisting of hydrocarbons and carbon; and imparting a high degree of mechanical energy to said particles within said molten metal to thereby force the impurities within the metal to the surface thereof, the mechanical energy of said particles being increased by the oxidation of said coating material with oxygen contained in said molten metal.

2. The process of claim 1 wherein the particles have a size range of between 5 microns and 225 microns and cause substantially complete dispersion of alloy substances throughout said molten metal, and cause impurities to rise to the surface of said metal.

3. A process for cleaning molten metal, which comprises: submerging a multiplicity of carbon coated particles having a size range of between 4 microns and 225 microns into a body of molten metal, said particles being lighter than said molten metal and having an alumina-silica core; and oxidizing the carbon on said carbon-coated particles within said melt to thereby deoxidize said molten metal and cause at least a portion of the heat energy produced by said oxidation step to be converted to mechanical energy to thereby increase the energy of said particles and force the impurities within the metal to the surface thereof.

4. A process for cleaning molten metals, which comprises: submerging a multiplicity of particles, having a size range of between 4 and 225 microns into the interior of a molten metal, said particles having an aluminasilica core, and an outer coating selected from the group consisting of hydrocarbons and carbon; increasing the mechanical energy of said particles within said molten metal to thereby force the impurities within said metal to the surface thereof, the mechanical energy of said particles being increased by the oxidation of said coating with oxygen contained in said molten metal thereby also deoxidizing said metal; and skimming the impurities from said melt.

:5. A process for cleaning, grain-refining and stabilizing molten metals having alloying substances therein, which comprises: submerging particles having an upper size limitation of 225 microns into the interior of said molten metal, said particles having an alumina-silica core, and a coating thereover selected from the group consisting of hydrocarbons and carbon; and increasing the mechani cal energy of said particles by means of chemical action between said particles and oxidizing gases in said molten metal, said increased mechanical energy being transferred to said particles to clean the interior of said metal by removal of the impurities to the surface thereof, said particles also cleaning the side walls of said vessel by frictional contact thereof with said side walls.

References Cited in the file of this patent UNITED STATES PATENTS 1,666,312 Runyan Apr. 17, 1928 2,237,485 Hardt Apr. 8, 1941 2,469,314 Ryland et a1. May 3, 1949 2,527,829 Leitten Oct. 31, 1950 2,578,605 Sears et a1. Dec. 11, 1951 2,760,859 Graf Aug. 28, 1956 FOREIGN PATENTS 19,012 Great Britain 1898 

1. A PROCESS FOR CLEANING MOLTEN METALS, WHICH COMPRISES: SUBMERGING A MULTIPLICITY OF PARTICLES INTO SAID METAL, SAID PARTICLES EACH HAVING A CORE CONSISTING ESSENTIALLY OF 10-30% ALUMINA AND 70-90% SILICA, AND A COATING THEREOVER SELECTED FROM THE GROUP CONSISTING OF HYDROCARBONS AND CARBON, AND IMPARTING A HIGH DEGREE OF MECHANICAL ENERGY TO SAID PARTICLES WITHIN SAID MOLTEN METAL TO THEREBY FORCE THE IMPURITIES WITHIN THE METAL TO THE SURFACE THEREOF, THE MECHANICAL ENERGY OF SAID PARTICLES BEING INCREASED BY THE OXIDATION OF SAID COATING MATERIAL WITH OXYGEN CONTAINED IN SAID MOLTEN METAL. 